1. Field of the Invention
This invention relates to a transparent piezoelectric transducer which employs a transparent piezoelectric ceramic material. This invention is very useful for microelectronic acoustic devices, and is applicable to the transducers of a watch, a radio, etc.
2. Description of the Prior Art
Recently, in microelectronic devices such as digital electronic wrist watches, the indication of a time etc. is not limited only to a visual form, but the aural indication of various functional factors including a specified time, an alarm, etc. has been required.
For example, the wrist watch is usually constructed of an optical display panel which is provided with a digital time display, a metallic case which supports the display panel and which protects a circuit portion, a transducer which is made of a piezoelectric material and which is mounted in the case, and a front glass plate which is stuck to be integral with the transducer. The transducer is excited by an electric signal from an electronic circuit, and the resulting vibration is transmitted to the glass plate to give forth, e.g., an alarm.
In such microelectronic devices, the miniaturization and the integration are required, while decorative factors are also involved, so that the utilization of transparent transducers which do not spoil the display effect when used in display portions has been attempted. Transparent piezoelectric vibrators have heretofore been seen in crystal resonators etc., but all of them are ordinarily operated in a higher frequency range. Among transducers which are operated in the audio-frequency range and used for sound production, voice production etc. requiring comparatively high power and which employ hard materials exhibiting comparatively stable frequency characteristics, there have been put into practice only ones which employ ceramic materials of the type of a lead lanthanum zirconate titanate solid solution (in general, called "PLZT").
An example of such transparent piezoelectric transducers is disclosed in Japanese Unexamined Published Patent Application No. 1978-55171.
Regarding the transducers, however, notwithstanding that the PLZT has been expected to exhibit a ferroelectricity and to have a great piezoelectric effect, any concrete product which positively applies the piezoelectric property thereof has not appeared yet.